Radio beacon system



am in, mu. mm: 2,1100? RADIO BEACON SYSTEM Filed June 12, 1937 I z I TRANSIH Patented Jan. 16, 194B parish stares.

FATE

6 Claims.

This invention relates to radio signal transmitting systems for transmitting signals in different directions for guiding movable craft, par- I ticularly aircraft.

An object of the invention is to provide different code signals in different sectors extending from a beacon point whereby a movable craft receiving such signals can determine from the nature of the signals received its position relative 'IO to the beacon point.

Another object is to produce code signals in different sectors extending from a beacon point of such characteristics that the code signals in H adjacent sectors will combine to produce on course signals of different code characteristics in a plurality of different on course positions.

'Another' object is to provide a simple and effective antenna system and antenna energizing i system for. producing different code signals in a plurality of dilierent directions extending from the antenna system from a single source of radio frequency energy.

The present invention involves improvements and modifications in the present well-known A and N radio beacon system in quite general use.

In the A and N system, an antenna system is employed which transmits radio waves modulated with the telegraph code for the letter A in two opposite quadrants and transmits radio waves. modulated with the telegraph code signal for the letter N in the other opposite quadrants. The dots and clashes representing the letter A are transmitted alternately with the dots and dashes representing the letter N so that in the region between each pair of adjacent quadrants where the radio waves, modulated with the dots and dashes representing the letter A overlap the radio waves modulated with the dots and dashes representing the letter N, the signals combine to produce an uninterrupted wave which produces a continuous sound in the receiver of an aircraft, thereby indicating that the craft is on one of four on course positions. A serious defect of the A-N system is that. a pilot receives the same signals in all four on course positions so that he cannot determine from the nature of the signal alone which of the four courses he may be on. Furthermore, since the same code signal is transmitted in each pair of diagonally opposite quadrants, the pilot cannot tell directly from the signal received which of two quadrants he is in.

. In accordance with the present invention, I overcome the serious defects described in the A-N- system by transmitting entirely different code signals in all four quadrants so that a pilot is immediately apprised by the code signal he receives in which of the four quadrants he is located. Further, in accordance with the invention, I so select and relatively time the code 5 signals transmitted in the four quadrants that the signals in at least several pairs of adjacent quadrants combine to produce different signals on the on course positions lying between the adjacent quadrants. 10

The invention will now be explained by describing in detail one specific embodiment thereof In the drawing: v

Fig. 1 is a schematic diagram of an antenna array and an antenna energizing circuit that 15 may be employed in practicing my invention.

Fig. 2 is a conventional diagram illustrating the shapes of the fields of radiation produced by the different sets of antennas in Fig. l.

Fig. 3 is a conventional diagram showing the 0 code signals produced in'various directions ex- I tending from a beacon, as illustrated in Fig. I.

Fig. 4 is a diagram showing the relative timing of the signals transmitted in different directions from the beacon illustrated in Fig. 1. 25

Referring first to Fig. I, there is disclosed in the upper portion of this figure an antenna array comprising eight different antennas ar-. ranged to be simultaneously energized in pairs for the directional transmission of radio signals 30,.

the antenna l but feeds to the antenna I through- 3-5 a phase shifter ill which shifts the phase of the radio frequency waves applied to' antenna l 180 with respect to the phase of the waves applied to antenna li' Antennas l and I when energized with radio frequency currents differ- 40 ing in phase by 180, produce a radiation field of figure eight characteristics as shown by the circles F1 in Fig. 2, the axis of maximum radiation being along a line interconnecting antennas l and l. 45

A second pair of antennas 2 and 2', positioned in a line parallel to a line interconnecting antennas l and l but positioned one-quarter wave length apart, are connected to a second feeder line L2. from the line L2 but antenna 2 is fed through a phase shifter H, which shifts the phase of the current in antenna 2 with respect to the phase of the current in antenna 2. It is wellknown that two vertical antennas positioned one- 55 In this case antenna 2' is fed directly '5 multaneous .of power illustrated as a motor 22.

quarter wave length apart and energized with currents differing in phase by 90 produce a field of radiation of cardioid shape in which maximum radiation occurs in one direction and minimum radiation in the opposite direction to the direction of maximum radiation, the directions of maximum and minimum radiation depending upon in which antenna the current is in leading phase relation. The phase shifter H is adapted to so control the relative phases of the currents in antennas 2 and 2 as to produce the maximum radiation in the direction of antenna 2' as shown by the shaded area F2 in Fig. 2.

The third pair of antennas 3 and 3, respectively, are separated one-half wave length apart along a line at right angles to the line interconnecting antennas l and i and are energized from 'a feeder line L3. The antenna 3 is supplied with current differing in phase by 180 from the current supplied to antenna 3 by virtue of a phase shifter l2 inserted between the feeder line L3 and antenna 3. Antennas 3 and 3, being energized by currents differing in phases by 180, as described, produce a radiation field of figure-8 outline, as indicated by the circles F3 in Fig. 2. The direction of maximum radiation is at right angles to the direction of maximum radiation of the fields F1 and F2.

The last pair of antennas d and l are spaced one-quarter wave length apart in a direction along a line parallel to a line connecting antennas 3 and 3' and are energized with currents differing in phase by 90 from a feeder line L4, the line L4 feeding directly to antenna l. and feeding to antenna 3 through a phase shifter 53. The relative phases of the currents in the antennas i and l are such as to produce a cardioid field pattern as indicated at F4 in Fig. 2, having a direction of maximum radiation in a direction looking from antenna 4' to antenna l.

The four sets of antennas described are all energized from a common source of radio frequency energy indicatedas a transmitter i5. In the purely schematic circuit of Fig. 1, the transmitter i5 is shown connected between ground I 6 and the various feeder lines L1, L2, L3, and L4 through a switching assembly ll. It is to be understood, however, that this particular method of energizing the antennas is adopted for the purpose of simplifying the drawing and that in. practice the transmitter l5 might better be connected to the Various antennas through transmission lines involving pairs of conductors, the ground connec tion for each antenna being made closely adjacent that antenna. Furthermore, the system may be employed with antennas functioning without ground connection in accordance with well-known practice in the art. The present invention does not reside in the exact way of ener gizing the antennas, but'rather in the use of antennas of particular radiation characteristics in combination with means for successively energizing different antennas in a particular sequence. The diagram of Fig. l-fully illustrates the sequence in which the various antennas are energized.

Theswitching system I! comprises three separate switches, each controlled by separate cams l8, l9 and 20, respectively, all mounted for sirotation on a common shaft 2! driven at a uniform speed by any suitable source Cam til has a lobe 23 extending half-way around and. a dwell 2G extending the rest of the circumference and has a follower 25 which is connected to a movable contact 28 cooperating with a back contact fl connected to transmission line L3 and a front contact 23 connected to transmission line L1. The cam 19 has a dwell 29 extending almost all the way around it and a short lobe 3B, the lobe being oriented as shown with respect to the lobe 23 of cam 20. Cooperating with the cam i9 is a cam follower 3! which is mechanically connected to, but electrically insulated from, a pair of electrical contacts 32 and 33, respectively. Contact 32 is connected to a main conductor 34 extending from the transmitter l5 and cooperates with a front contact 35 connected to the transmission line L4. Contact 33 cooperates with a back contact 36 connected to contact 26 associated with cam 20.

Cam it, like. cam i9, is provided with a long dwell 3'7 and a short lobe 38 but the lobe 33 is so oriented with respect to the lobe fall of cam NJ as to lift the cooperating cam follower 39 substantially later in the cycle of operations than the follower 3! is lifted by lobe 3!]. Cam follower 39 is mechanically connected to, but electrically insulated from, a pair of contacts li} and ll, respectively. Contact 40 is connected to the main supply conductor 34 and cooperates with a front contact 42 connected to transmission line L2. Contact 4| is likewise directly connected to the main supply conductor 34 and cooperates with the back contact 53 which is connected with the contact 33 associated with cam 39.

The lobe 30 on cam cam l8 each extend of the circumference of i9 and the lobe 38 on the cams I9 and i8, respectively, and thereby raise their associated cam followers 3| and 39, re-.

spectively, during of a revolution of the shaft M. The shaft revolves at such a speed that the lobes 3i! and 3B maintain. their followers 3! and 39, respectively, in elevated position for a period of time required to transmit a radio signal having a duration equivalent to one dot in the Morse code. The lobe 23 on cam 20 extending one-half way around the cam raises the follower for a period five times as long as the followers 8! and 39 are lifted.

With the shaft 2! in the position shown, with ing energizing current to antennas l and I of such phase relation as to produce the field pattern F1 in Fig. 2. This condition will maintain while shaft 2! rotates through of a revolution. During rotation of shaft 2! through the next T16 of a revolution lobe lifts cam follower 3| to break connection between the main supply conductor 3t and the conductor L1 at the contacts 33 and 36 and to connect the conductor 34 through contacts 32 and to the conductor L4, thereby energizing antennas 4 and A in proper phase relation to produce the field pattern F4 in Fig. 2 during the time interval represented by one dot in the Morse code.

During the next of a revolution of the shaft 2!, follower 3! is again in lowermost position and follower 39 is still in lowermost position. whereas follower 25 is still in upper position. thereby again applying the transmitter output to the conductor L1 and the antennas I and l to again produce the field pattern F1 in Fig. 2 for the interval of one dot. During the next revolution all three followers 25, 3| and 39 are in lower position, thereby applying current from iii) conductor 34 through contacts 4!, 43, 33, 36, 26 and 27 to conductor L3, energizing antennas 3 and 3' to produce the field pattern F3 in Fig. 2 for the interval of one dot. During the next following 1,- revelution the lobe 38 of cam 58 elevates the follower 35 to connect conductor 34 through contacts 5 and 42 to conductor L2, thereby energi m2 antennas 2 and 2 to produce the field pattern in Fig. 2 for an interval of one dot after which follower 39 drops off lobe 38 and for the next three-tenths of a revolution of shaft 2! all three followers 25, 33, and 29 are in lowermost position, thereby connecting con ductor as through contacts 4!, i3, 33, 56, 28 and 2'! to conductor L3 to energize antennas 3 and 3. and produce the field pattern F3 in Fig. 2 for an interval of three dots. During the next three-tenths of a revolution (which restores the shaft 2| to the starting point), the follower 25 is in elevated position, While followers 33 and 39 are in lowermost position, thereby connecting conductor 34 over contacts 46, 43, 33, 36, 26am. 8 to conductor L1, energizing antennas i and l to produce the field pattern F1 in Fig. 2 for an interval of three dots.

Referring now to Fig. 3 this diagram shows the nature of the signals that will be transmitted in different directions from the general location ii of the antenna system shown in Fig. l in response to the operation of the switching systern, and directive antennas described. The area surrounding the antenna location 6 is shown di vided into four large segments Q11, Qd, Qu and Qn, respectively. these segments being hereinafter referred to as quadrants. Small segments Cad, Cdu, Gun, and C1121, interposed between the four quadrants, will be hereinafter referred to as courses. The signals produced in the quadrant Q's. result only from field F3 in Fig. 2. The signals produced in the opposite quadrant Q are produced by both field F3 and field F4. The signals produced in quadrant Qn result only from field F1 and the signals in quadrant Qu result from the fields F1 and F2.

The signals that will be heard in course C are the combined signals produced by the over- The signals produced in course Cdu will ping fields F3 and F1 and F4 and F2. The signals produced in the course Cun will be the combined signals resulting from the overlapping fields F1, F3 and F4.

Referring now to Fig. ithe horizontal row of dots and dashes, identified by the letter D. represent the sequence of signals transmitted in the quadrant Q1 of Fig. 3; the horizontal row of dots and dashes opposite the letter U represent the sequence of signals transmitted in the quad rant Q of Fig. 3; the horizontal row of dots and dashes opposite the letter N represent the se quence of signals in the quadrant Qn of 3;

= and the horizontal row of dots and dashes opposite the letter A represent the sequence of signals in the quadrant Qa of Fig. 3. It will be noted that if the dots and dashes in row D of Fig. 4 are added to the dots and dashes in row U a continuous signal DU results which will indicate the signal transmitted along course Cdu in Fig. 3. If the impulses in rows U and N of 4 are added, the resultant signal UN is a series of long dashes separated by single spaces, which is the signal transmitted in course Cun.

als produced by overlapping fields F3, F1

Referring again to Fig. 4, if the signal impulses in row N are added to the signal impulses in row A, the resultant signal NA consists of alternate long and short dashes separated by a single space. This-is the signal which exists along course Cut in Fig. 3. If the signal impulses in row A and the signal impulses of row D in Fig. 4 are combined, the resultant signal AD is a series of long dashes separated by short spaces identical with the signals UN.

The production of the signals as shown in by the system shown in Fig. 1, may be readily followed through by observing that the shaft 28 in Fig. l is in the position shown at the instants To, T10, and T20 indicated in Fig. 4, the latter figure showing the signals produced during three complete cycles of operation of the cam mechanism in Fig. 1.

It will be apparent from the foregoing discussion that the dot-dash signal representing the letter A will be repeatedly transmitted in the quadrant Qa of Fig. 3, and that the dash-dot-dot signal representing the letter D will be repeatedly transmitted in the quadrant Qd. These signals, overlapping each other in the course Cm will produce in that course a series of long dashes separated by single spaces. The code signal dotdot-dash, representing the letter U, will be repeatedly transmitted in the quadrant Q11 and these signals willcornbine with the dash-dot-dot signals of quadrant Qd to produce in the course Cdu a continuous, steady signal. The code dashdot representing the letter N will be repeatedly transmitted in the quadrant Qn and these signals will combine with the dot-dot-dash signals of quadrant Q to produce in the course Cun a series of long dashesseparated by short spaces similar to the signals produced in course Cad. The dot-dash signals in quadrant Ca will combine with the dash-dot signals in quadrant C to produce in the course Cna a signal consisting of alternate short and long dashes separated by single spaces.

It will be apparent, therefore, that a different code signal will be received in each of the four quadrants Q3, Qd, Q and Qn. Likewise difierent code signals will. be produced along the three courses Cna, Cad, and Cdu- With the system shown, however, the code received along the course Cun will be the same as that received along course Cad- Zt will be observed that the dot-dash code signal for the letter A. produced in quadrant Q8. results solely from energization of antennas 3 and 3 in Fig. l and that the production of the dash-dot code signal in quadrant Qn is produced entirely in response to ene-rgizati-on of the antennas i and l in Fig. 1. However, the dot-dotdash code signal transmitted in quadrant Qu is produced by both antennas 3 and 3' and antennas 6 and 5-. Thus the antennas Al and l, which produce the cardioid field F4 in Fig. 2, transmit the first dot of the signal, which dot is not transmitted in quadrant Qa because of the unidirectional characteristics of antennas 4 and 4". The remainder of the signal in the quadrant Q is a dot'and dash identical with the complete signal in quadrant Qanal for the letter U of quadrant Q11 is co1npleted by adding to the dot transmitted from antennas Al and i the dot-dash which is transmitted in two directions from antennas 3 and 3'.

Similarly, the dash-dot signal in the quadrant Qn and the dash-dot-dot signal in quadrant Qd are produced by first transmitting a dash-dot in Therefore the code sigboth directions from antennas i and l and then transmitting one dot only in the direction of quadrant Qd from the unidirectional antenna array comprising antennas 2 and 2'.

In Fig. 2, for purposes of'clarifying the diagram, the cardioid field patterns F4 and F2 are shown of lesser extent than the juxtaposed lobes of the figure-8 patterns F3 and F1, respectively, However, it is to be understood that in practice the field strength of the fields F4 and F2 will be substantially the same as those of fields F3 and F1.

For the purpose of explaining my invention, a specific embodiment thereof has been indicated schematically and described in detail. However, it will be apparent to those skilled in the art that numerous changes and modifications can be made in the particular arrangement shown, and the.

invention is therefore to be limited only as set forth in the appended claims. It should be noted particularly that other code signals and other combinations of code signals than those disclosed, may be employed.

I claim:

1. The method of producing a radio range having differently coded signals in diagonally opposite sectors, which comprises transmitting a radio wave simultaneously in two diammetrically opposite directions to produce a complete unitary code signal in one sector and part of a different unitary code signal in the opposite sector, and transmitting a radio wave in said opposite sector only to complete said different code signal in said opposite sector.

2. A radio beacon comprising a first means for transmitting signals predominately in one direction only and a second means for transmitting signals equally in two opposite directions, one of which directions is the same as the direction of transmission of said first means, means for energizing said two transmitting means alternately in predetermined timed relation to repeatedly transmit a single predetermined different code signal in each of said two opposite directions, the signal transmitted in said one direction only supplementing the signal transmitted in both of said directions to form the single predetermined code signal transmitted in said one direction.

3. A radio beacon comprising a first means for radiating waves predominately in one direction, a second means for radiating waves equally in two opposite directions, one of which is the same as said first direction, a third means for radiating waves predominately in one direction at a substantial angle to said first direction, and a fourth means for radiating waves predominately in two opposite directions, one of which is identical with said third direction, and means for successively and repeatedly energizing said four radiating means in predetermined order to repeatedly transmit a single predetermined different code signal in each of said four different directions.

4. The method of producing a radio range having different identification in different sectors in a horizontal plane, comprising: transmitting radio waves horizontally in a plurality of overlapping sectors from a central point, differently interrupting the waves transmitted in two overlapping sectors to produce different telegraphic code signals in said two different sectors, the signals in the two sectors being complementary to each other, whereby the radio wave is continuous in the region of overlap, and differently interrupting the waves in the two respective sectors of a second pair of sectors to form code telegraph signals that are relatively short and not completely complementary whereby the radio wave is discontinuous in the region of overlap of said second pair of sectors.

5. A radio beacon comprising: means for transmitting a telegraph code signal in a first quadrant, means in addition thereto for transmitting a second code signal in the third quadrant diagonally opposite said first quadrant, which second signal includes as a component thereof the same signal transmitted in said first quadrant, means for transmitting a third code signal in the second quadrant between said first and said third quadrants different from the code signals in the first and third quadrants, and means in addition thereto for transmitting a fourth code signal in the fourth quadrant diagonally opposite said second quadrant, which fourth signal includes as a component thereof the same code signal transmitted in said second quadrant.

6. A radio beacon comprising means for radiating a plurality of overlapping sectors of directionally radiated energy, defining courses in the regions of overlap, means for characterising pairs of sectors of energy by identical signals, the sectors of each pair being oppositely disposed, and

eans for radiating additional signals in one of each pair of said sectors to change the identity of the first-mentioned signal therein and give a unique signal of identification to each sector.

FRANCIS POPE. 

